The present invention relates to a color television camera using a solid-state image pickup device and a color filter array.
Color television cameras using solid-state image pickup devices such as CCD, CID and MOS have been actively developed in recent years. Particularly, a so-called single chip type color television camera has attracted noticeable attention in this field. In this type of color television camera, color filters are arranged corresponding to the number of picture elements. An optical image modulated by the color filter is applied to the solid-state image pickup device. Then, the image pickup device separates the image into three primary colors.
The prior art employ a number of color filters of three colors, i.e. red, blue, and green, which are arranged as shown in FIGS. 1 and 2. FIGS. 1 and 2 show patterns or arrangements of color filters in the color filter arrays as matrix arrays of the color filters. In the pattern shown in FIG. 1, pairs of green filters are arranged in a mosaic fashion in the vertical scanning direction. The remaining spaces of the matrix color filter array are alternately filled with pairs of the red and blue filters every two rows. In the filter pattern of FIG. 2, pairs of the green filters are arranged in a mosaic fashion, like the filter pattern shown in FIG. 1. The remaining spaces in the matrix array are filled with pairs of the red and blue filters in every column, as shown. In both the filter arrays, two of the same color filters are continuously arranged in successive order, as shown. The reason for this is that the color filter array is designed for an interlaced scanning system. In these examples, signals are taken out every two rows in one field scanning. The green color signal provides a major part of a luminance signal. Therefore, it is desired to use as large a number of green color signals. Drop-out of the green signals occurring in one line scanning is compensated for by scanning two lines, with an increase in the number green signals used. For obtaining a more complete signal, even four lines of scannings are required. On this basis, the prior art color filter arrays as shown can provide an unsatisfactory resolution in the vertical scanning direction.
Red and blue color signals are produced in a line-sequential order. The line sequential color signals must be converted into concurrent signals. To this end, these color signals must be delayed one horizontal scanning period, using a so-called 1H delay line. When the color of an object under image pickup abruptly changes from one color to another in the vertical scanning direction, because of the delay of one horizontal scanning period, the colors before and after the color is changed occasionally overlap becoming a concurrent signal which is a false signal. The presence of the false signal markedly impairs the picture quality of the reproduced picture.
For separating three primary colors from the color signals, multiplex color signals from the solid state image pickup device must be gated at specific phases thereof. When a signal transmission path has a narrow frequency band, a switching circuit associated with the gates must be operated in a high frequency mode. Such a switching circuit is complicated and needs large power consumption. Reliable color separation is also difficult. Occasionally, color fidelity deteriorates in the reproduced picture.
The problems as mentioned above are common to both the prior color filter arrays shown in FIGS. 1 and 2. Particularly, the color filter array of FIG. 2 has the following disadvantages. The color filter patterns of the color filter array of FIG. 2 provide red and blue color signals every four color filter rows. The frequency of the carrier wave is therefore lower than that of the color filter pattern of FIG. 1. This indicates that the frequencies of the red and blue signals fall within the frequency band of the luminance signal. The likelihood is that stripe noise possibly appears in the reproduced picture. For example, if the color of the object under image pickup is red over its entire surface, excessive charges are produced in the picture elements of the solid-state image pickup device, which correspond to the red color filters. The excessive charges produced overflow into the picture elements corresponding to the green color filters adjacent to the red filters. The result is that the camera operates as if the green color signals are produced. Actually, a periodical shade appears in the reproduced picture, because the green color signals make the greatest contribution to the formation of the luminance signal. The red color signals appear in the form of shaded stripes in the reproduced picture. For improving resolution, high frequencies are usually emphasized. In such a case, even if the above deleterious phenomena could be eased by some measure, a slight amount of color mixing is still a problem. This fact prohibits the emphasis of high frequencies a clear picture cannot be produced.
The prior art color filter arrays also involve problems in the manufacturing process. In manufacturing the prior art color filter arrays, the color filters are colored with three primary colors in successive order. This process requires a number of steps to manufacture. This leads to an increase in the manufacturing cost. Further, dirt tends to stick to the filters under manufacture. Thus, the prior color filter arrays suffer from a high rate of defective products, or a poor production yield, and thus increased manufacturing costs.